1. Field of the Invention
The present invention relates to a method and an apparatus for surface-treating the inner surface and/or the outer surface of a half sliding bearing.
2. Related Art
Hitherto, the inner surface of a half sliding bearing is applied with electric plating to form a plating layer of several microns to several tens of microns in thickness in such a manner that an anode bar is disposed in the axial direction along the center line of the inner surfaces of a plurality of half sliding bearings placed in a tank in which a surface-treatment solution is enclosed. In this case, the upper and the lower portions of the half sliding bearing generate the portion in which the desired plating thickness cannot be obtained. Accordingly, members, each of which is so-called a spacer metal or a dummy metal in the form of a half sliding bearing and made of a conductive material, are fastened to the upper and the lower portions of the half sliding bearings. Then, a plating case to which the half sliding bearings have been fastened is treated in a degreasing tank, an electrolytic degreasing tank, an acid dipping tank, a plating tank, a recovery tank, a water rinsing tank, a neutralization tank and a cleaning tank and the like. The treated hale sliding bearings are then removed from the case so that the surface treatment for the half sliding bearings is completed.
However, the conventional technology has encountered the following problems:
(a) The case or a jig to which the plurality of the half sliding bearings have been fastened is dipped into the treatment solution so as to be treated as desired before the half sliding bearings are taken out. However, the quantity of undesirable discharge of the treatment solution is enlarged in proportion to the surface area of the object to be introduced and taken out. The undesirable discharge will enlarge in quantity in proportion to the degree of complication of the structure of the plating case and the like. Therefore, a problem arises in that each of the treatment solution is contaminated due to the rise in the density of the recovered treatment solution, that is, the contamination concentration of the rinsing water. What is even worse, the quality of the plating will deteriorate and problems in terms of the waste water disposal will take place. PA1 (b) In order to uniformly supply electricity to the half sliding bearings, a uniform contact with the power supply portion of the plating case or the jig is necessary. However, there are too many contact portions such as the contact portion between the half sliding bearing and the spacer, that between the spacer and the plating case or the jig and that between the plating case or jig and the hooks of the apparatus. Therefore, the uniform electricity supply is hindered by the total quantity of the contact resistance. As a result, the accuracy in the plating thickness is deteriorated. PA1 (c) Furthermore, the vertical position of the half sliding bearing in the plating case or the jig will cause the change in the electric current distribution characteristics. Hitherto, a method as shown in FIGS. 7A and 7B has been employed in order to reduce the above-described undesirable change in such a manner that spacers 101 each having the same inner diameter as that of the half sliding bearing are disposed in the upper and the lower portions at the time of the electric plating. However, the above-described change has not satisfactorily be prevented. What is even worse, the accuracy in the thickness of the plating will deteriorate due to the inclination of the plating case or the like. PA1 (d) The spacer 101 employed in the manner as described above must be provided for each of the plating cases or the jigs to which a plurality of the half sliding bearings are fastened. Since the spacer 101 is subjected to the plating at each of the plating operations, its surface will be gradually raised and the surface will become too rough. It leads to a fact that the accuracy in the thickness of the plated layer at the portion of the half sliding bearing adjacent to the spacer is deteriorated. Furthermore, another problem arises in that each of the treatment solution is contaminated due to the rise in the concentration of the recovered treatment solution, that is, the contamination density of the rinsing water. What is even worse, problems in terms of the waste water treatment will take place. PA1 (e) According to the conventional method, insoluble sediment adheres to the jig and the quantity of the sediment is enlarged due to a chemical reaction simultaneously with the occurrence of the contamination described in (a) during a period in which the plating case or the jig is dipped in the alkali solution and the acidic solution. Furthermore, since each of the treatment solution is arranged to be used at an individual temperature, the case or the jig must be subjected to a repetition of high temperature and low temperature. As a result, a strain generates in the case or the jig, causing the accuracy in fastening the half sliding bearing to be deteriorated. What is even worse, the accuracy in the thickness of the plating applied to the half sliding bearing is deteriorated. PA1 (f) Since the performance of the engine must be improved and the noise from the same must be reduced in recent years, the half sliding bearing and the surface of the half sliding bearing must be finished extremely precisely. Furthermore, there is a desire for the half sliding bearing to reveal a uniform quality. Therefore, a rigid plating case, a large-size plating apparatus and a large-size wastewater disposal facility are necessary for the above-described conventional methods. Furthermore, a large quantity of water must be supplied. As a result, this, of course, excessively raises the initial cost, the running cost and the cost for the maintenance. PA1 (g) Another problem arises in terms of the manufacturing operation such that too many operations, such as operations of fastening the half sliding bearing to the case, fastening the case to the apparatus, removing the same from the apparatus and drawing out the half sliding bearing from the case, must be repeated. Therefore, an excessively large cost is necessary to complete the above-described repetitive operations if the above-described operations are performed by humans or automatic apparatuses. Therefore, the manufacturing cost has not been reduced.